Flow regimes and reactivity assessment in arrow- and X-microreactors: a combined numerical and experimental approach

In this study we use numerical simulations and experimental investigations to gain a comprehensive characterization of the flow dynamics inside microreactors. Two different simple geometries, namely the arrow- and the X-microreactors, are considered, both fed with reactive liquid streams. In both geometries, at low Reynolds number, Re, the streams stratify in the outlet channels due to the different densities of inlet solutions. At Re around 50, the X-microreactor exhibits a single central vortex in the mixing channels, leading to a highly mixed flow regime. By increasing the Reynolds number, the vortex elongates in the outlet channels and increases in size. Conversely, in the arrow-microreactor, three different flow regimes occur before transitioning to unsteady flow: the vortex, the engulfment, and the single-vortex regimes. Unlike the X-shaped geometry, the engulfment regime in the arrow geometry is characterized by the presence of two corotating vortices that extend in the outlet channel. The reaction yield is evaluated and compared in the two geometries, showing that higher performance is achieved when a single central vortex is present in the outlet channels.